The energy consumption of an integrated circuit can be reduced by dynamically reducing the supply voltage when the operating mode permits such a reduction. Indeed, reducing the supply voltage has an effect on the performance of the circuit, reducing the maximum frequency at which the circuit is capable of operating. By dynamically controlling the supply voltage and the operating frequency of the circuit, a trade-off between energy consumption and performance can be achieved based on the particular needs of the operating mode.
The PVT point of a circuit corresponds to levels of the three main parameters that influence performance: process, voltage and temperature. If the PVT point of a circuit can be estimated at any given time, this allows the transistor speed to be deduced, and thus the operating frequency and/or supply voltage can be set in order to achieve a desired performance.
Solutions exist for estimating the PVT point. For example, some solutions are based on ring oscillators that generate an oscillating signal at a frequency that depends on the PVT point. However, such circuits tend to be complex and slow, occupy a relatively large chip area and have relatively high energy consumption.
An example of a circuit for which an estimation of the PVT point would be beneficial is an SRAM (static random access memory). Indeed, it has been proposed to provide voltage assistance techniques to permit read and write operations to an SRAM to be performed successfully in the presence of very low supply voltage levels. However, such techniques are only useful in the case that the supply voltage within the circuit is not sufficiently high to support standard operation. The activation of the voltage assistance techniques is generally performed by an external circuit, which has relatively imprecise information regarding the PVT point within the SRAM. Furthermore, the use of an external circuit requires I/O (input/output) pins, whereas it is generally desirable to limit the number of pins.